As a method for forming an insulating film such as a silicon oxide film and a nitride film in a transistor element isolation region or an interlayer insulating film between wirings in a semiconductor manufacturing process, a thermal CVD method is usually used to form a high-quality insulating film in the case where a high-temperature heat treatment at 750° C. or more is allowed in the process. In addition, in the case where a high-temperature heat treatment at 450° C. to 750° C. is allowed in the process, a thermal CVD film is formed at a temperature of 420° C. to 500° C. by CVD method at a normal-pressure, and then the quality of the insulating film is improved by a heat treatment at about 750° C. in general.
Recently, it is highly required to operate an element such as an LSI (large-scale integration) and a CCD device at higher speed, and to miniaturize a manufacturing process to implement low power consumption, and to improve the quality of the insulating film such as the silicon oxide film and the nitride film formed in the transistor element isolation region or the interlayer insulating film between the wirings (that is, to improve the electric characteristics shown by withstand voltage and leak current characteristics in general). In general, it is known that a CVD oxide film and a CVD nitride film formed by a film forming method of a low-temperature CVD method where the assist of active oxygen such as plasma and ozone is necessary, is inferior in film quality (electric characteristics here) to a film formed by a HTO-CVD method such as a thermal CVD method, in a process after a gate forming step (BEOL) in a semiconductor element such as an LSI and a CMOS image sensor in which a metal (metal material) having a low melting point (450° C. or less) is used as a gate wiring material of a transistor. In addition, it is known that according to a plasma CVD film formed by a plasma CVD method, the characteristics of a formed transistor deteriorates in a latter process (BEOL) due to damage caused by plasma processing.
A patent literature 1 (PTL 1) discloses a film forming method in which a film with less oxygen deficit can be formed easily at low cost. A mixed gas contains an organic metal compound gas, an oxidizing gas, and a rare gas (inert gas). A proportion Pr of a partial pressure of the rare gas in the mixed gas is 85%≦Pr<100%. The mixed gas is introduced in a plasma processing chamber. According to the technique, plasma is generated in the plasma processing chamber, and the organic metal gas and the oxidizing gas are decomposed by the plasma to form a metal oxide film on a target substrate.
A patent literature 2 (PTL 2) discloses a film forming method in which a silicon base oxide film is formed on a target substrate uniformly while preventing plasma damage given to the target substrate or the silicon base oxide film formed on the target substrate. A mixed gas containing an organic silicon compound gas having silicon atoms, carbon atoms, and oxygen atoms in at least one molecule, an oxidizing gas, and a rare gas having at least one kind or more among argon, krypton and xenon in which the proportion, Pr, of the partial pressure of the rare gas becomes 15%≦Pr≦85% is supplied into a plasma processing chamber. According to the technique, plasma is generated in the plasma processing chamber, and the organic silicon compound gas and the oxidizing gas are decomposed by the plasma to form a silicon oxide film on the target substrate. In addition, as a plasma source, a parallel plate type plasma source is used.